The link between erythema ab igne and internal malignancy has not been emphasized in recent years; published reports have focused mainly on devices that may cause the characteristic cutaneous pattern of reticulated hyperpigmentation or on cutaneous malignancies arising in longstanding erythema ab igne. Our goal in this correspondence is to emphasize the critical value of erythema ab igne in detecting occult malignancy.

We evaluated a 66-year-old woman for a rash on her mid-back characterized by reticulated hyperpigmentation (Fig. 1a) and diagnosed as erythema ab igne. The patient reported chronic back pain of at least four months' duration, for which she was applying a hot-water bottle several times per day in order to achieve pain relief. After making repeated visits to an emergency room for the back pain and having reported a weight loss of 13.6 kg, the patient underwent a computed tomography scan of the abdomen and pelvis, which revealed a mass in the head of the pancreas (Fig. 1b, c). Endoscopic ultrasound with biopsy confirmed a diagnosis of pancreatic adenocarcinoma.

Figure 1.

(a) Erythema ab igne on the back in a 66-year-old woman was a clinical sign of underlying pancreatic cancer. (b) Computed tomography of the abdomen and pelvis shows pancreatic adenocarcinoma encasing the celiac axis (red arrow). (c) The hypoattenuating pancreatic disease also obstructed the common bile duct and pancreatic duct (orange arrows)

Erythema ab igne is reticulated erythema and hyperpigmentation localized to an area of skin that is chronically exposed to heat; typical heat sources include heating pads or devices, hot-water bottles, close proximity to fireplaces, and, most recently, laptop computers.[1, 2] The presence of erythema ab igne requires that a history be elicited from the patient. If a patient reports that chronic pain underlies his or her regular use of a heating device, a complete review of systems should be obtained, and the patient should be referred to primary care for further evaluation. When systemic symptoms are present, underlying disease including pancreatitis[3] and primary or metastatic malignancies[4-7] must be considered.

In the present patient, erythema ab igne on the middle part of the back was a sign of the significant use of a hot-water bottle in the treatment of chronic lower back pain in the context of recent weight loss; the patient's subsequent evaluation revealed pancreatic cancer. An analysis of reported cases in which erythema ab igne served as a clue to internal malignancy (Table 1) revealed that the majority of malignancies (six of 11, 55%) were gastrointestinal (colorectal, pancreatic, gastric); less common etiologies were lung, renal, breast, and hematologic malignancies. In all of these cases, erythema ab igne was located in the skin either at the site overlying the affected organ(s) or at the site of referred pain.

In summary, although erythema ab igne is benign, it can be associated with cancer in two different ways. More commonly, it represents a risk factor for the development of cutaneous malignancies within longstanding erythema ab igne, such as squamous cell carcinoma,[8] Merkel cell carcinoma,[9] or lymphoma.[10] Less commonly, it portends an occult internal malignancy. This correspondence aims to improve recognition of the latter scenario, in which a history of underlying chronic pain should elicit a complete review of systems and further evaluation by a primary care physician. Although it is not a sign, per se, of systemic disease, erythema ab igne sometimes marks an underlying internal malignancy, and the astute clinician will not dismiss this otherwise benign rash.